The design of Polyroad stabilised pavements is to preserve the existing dry strength pavement properties and resist the ingress of water which is the major cause of pavement failure. Polyroad binders were first incorporated into pavements in Australia in 1988 and have since been extensively used in National and State Highways in Australia and parts of Asia.
Polyroad consists of an insoluble polymer thermally bound to an ‘inert fine carrier’, typically fine ground lime. The polymer encapsulates the fine ground lime rendering the fine ground lime inert and does not react chemically in the stabilisation process. Hydrated lime is added to the polymer-coated carrier but is not coated with the polymer. The lime’s function is to flocculate and prepare clay particles for adhesion to the polymer rather than generate pozzolanic cementitous bonds.
Loading Polyroad into pneumatic road tanker.Polyroad binder types are dependent upon the plasticity index (PI) of the parent material to be stabilised as follows:
- Polyroad PR100 is 100% polymer-coated fine inert carrier, spread at a rate of 1%, and is used with materials that are non-plastic.
- Polyroad PR21L is spread at a rate of 1.5%, containing 67% polymer and 33% hydrated lime, and is for materials with a PI of 12% or less. The 33% of lime in the blend is only to open up clay plates to then be coated with the polymer – not to perform pozzolanic reactions as typically associated with lime stabilisation.
- Polyroad PR11L is spread at a rate of 2%, containing 50% polymer and 50% hydrated lime, and is for materials with a PI of 12% to 20%. Again the lime is only required to break open the clay plates for polymer attachment.
Water droplets on Polyroad stabilised pavement, Yass. Photo by M.Greaves, CSIRO Clayton, Vic.Polyroad’s ability to perform without pavement misshape or maintenance repair to date, is predominantly a result of no plastic deformation occurring within the pavement because of the ‘internal’ waterproofing of fine grained particles that Polyroad provides.
Polyroad stabilisation has been used by New South Wales, Victorian, Queensland and Tasmanian State Road Authorities and numerous Local Government Authorities in New South Wales and Victoria.